Syringes are widely used to administer drugs or other substances, to withdraw body fluids, or to dispense liquids for a variety of medical and other purposes. A syringe typically comprises a cylinder, a piston that is reciprocable in the cylinder and protrudes from an open end thereof, and a needle attached to the other end of the cylinder. Almost universally, such syringes are currently mass produced from a low-cost material, e.g. by molding the syringe and the piston from plastic materials such as polypropylene. The needle is made of a suitable material such as surgical steel and includes an adapter so that it can be attached to the the syringe.
For many applications, a conventional syringe, which has a plunger that reciprocates linearly in the syringe, is sufficient because there is no need to precisely control the amount of liquid that is drawn into or ejected from the syringe.
At other times, however, a precise control of the amount of liquid leaving or entering the syringe is necessary for reasons of health, cost of the dispensed liquid or otherwise. A syringe having a manually operated, linearly reciprocable piston cannot provide this control. Instead, such applications require syringes in which the piston is moved in the cylinder in precisely controlled increments, e.g. a Vernier-type syringe. Typically, such syringes are relatively complicated to construct and maintain. Moreover, the person using the syringe, e.g. a physician should have both types of syringes available to be prepared for any eventuality that may arise. When this is not the case complications may arise at the critical moment when the syringe is needed.
A further complicating factor is that syringes which permit a precise metering of the amount of liquid that is dispensed are relatively costly. Unlike conventional syringes, they are not normally throwaway items. Instead, they must be cleaned and sterilized after each use. Thus, a physician, for example, either requires a supply of several such syringes or he can use a single such syringe only at spaced time intervals, i.e. after a used syringe has been cleaned and sterilized. The former alternative is cumbersome in practice and relatively expensive; the latter alternative is undesirable and in certain situations, such as when a physician makes a number of calls at the same time, outright unacceptable.
To overcome this dilemma, applicants have disclosed in a commonly owned co-pending patent application an adapter to convert low-cost conventional, throwaway syringes into a Vernier-type syringe by substituting an exteriorly threaded piston for the conventional piston of the syringe, or by appropriately modifying the latter so that it has an exterior thread. Further, a mechanism is attached to the open end of the syringe which can engage the piston thread and requires that the piston be rotated about its axis to reciprocate it in the cylinder.
The present invention extends the concept disclosed in the co-pending patent application. As in the co-pending application, the present invention makes it possible to use a syringe in two modes. First, it can be used by conventionally linearly reciprocating the piston in the cylinder, hereinafter usually referred to as the "linear mode". Second, it can be used by requiring that the piston be rotated about its axis to reciprocate it in the syringe, hereinafter usually referred to as "Vernier mode". Additionally, the syringe can be operated incrementally by rotating the piston as in the Vernier mode but generating a signal each time the piston has rotated through a predetermined arc, hereinafter sometimes referred to as the "incremental mode". However, the present invention does not employ an adapter to convert a conventional syringe into a Vernier syringe. Rather, it provides a syringe which is both, i.e. which has the three alternative operating modes without, however, requiring a separate adapter that must be fitted to the syringe.